The roads ahead

The Transport Research Laboratory's Michael McHale and Bob Collis outline their vision for how our roads should be designed, built and operated in the future

The importance of addressing the challenges of sustainable development and climate change cannot be overstated. In the transport domain, it is essential to adapt and embrace new technologies that will bring about immediate benefits to road operators and users. The Transport Research Laboratory (TRL) is one organisation working to achieve this at both the regional and international level.

New surface course specification

In Scotland, it is hoped that a new surface course specification, developed by Transport Scotland and TRL for the Scottish Trunk Road Network, will help to deliver significant improvements in material durability and cost savings, which ultimately will result in less disruption to road users generated by road construction and maintenance.

The new specification marks a step change for specifying surfacing material. It has been developed in response to concerns raised about the in-service performance of various proprietary 'thin surfacings'. There had been several reported incidences of new surfacing deterioration after only short periods and that the top layer of road surfacing did not represent good value for money.

In addition, safety concerns were expressed regarding the presence of excess bitumen binder that could lead to a reduction in early life skid resistance and is, of course, an avoidable cost.

So how did the new specification come about? In 2007, the Transport Scotland Pavement Forum (TSPF) was created to encourage two-way communication between clients, designers and suppliers/contractors and to promote, develop and implement best practice across the road industry.

One of the first TSPF initiatives was to set up an annual surfacing monitoring and reporting programme in 2008. The Scottish Inspection Panel (SIP) report provides a yearly indicator of in-service performance against expectations, and identifies areas of good practice and typical modes of failure. This resulted in a major SIP recommendation that efforts should be made to reduce the open texture appearance of surfacing by exploring the use of denser mixes utilising smaller stone aggregate sizes.

Drawing on experience from Germany, where the use of smaller aggregate sizes and higher bitumen binder content is used to enhance material durability, a series of road trials were set up. Study visits were also made to Germany both before and after the trials, initially to gain knowledge and then to refine development.

It was found that the smaller stone mixes with a thicker binder coating resulted in an expected service life of 16 years, with many heavily trafficked sites providing 20 years of service.

As a result of this work, Transport Scotland has been able to give final approval to a new surface course specification for the Trunk Road Network in Scotland. The specification covers a range of aggregate sizes (14, 10, 8 and 6mm) that will enable the use of all sizes of aggregate materials, thereby reducing waste. This new approach will bring two key benefits in terms of improved material durability and value for money, something to be welcomed at a time of reduced funding.

Importantly, road users should suffer less disruption to the network caused by construction and maintenance works, resulting in less congestion and a reduction in CO2 emissions.

The Forever Open Road

The Forever Open Road programme is at the heart of FEHRL's Strategic European Road Research Programme (SERRP V).¹ Based on a concept originated by TRL, it centres on developing a new generation of roads that are adaptable, automated and resilient to extreme weather events.

The Adaptable Road will be fully adaptable to changes in demand. It will be based on a prefabricated/modular system that can gradually be implemented across Europe's motorway, rural and urban road networks. It will adapt to increasing travel volumes and to changes in demand for public transport, cycling and walking. Additionally, it will power vehicles, harvest solar energy, measure its own performance and even repair itself.

The Automated Road will be fully integrated with the user, vehicles and operations. It will incorporate a fully integrated information, monitoring and control system, enabling communication between road users, vehicles and operators. It will also support a cooperative vehicle-highway system that will manage travel demand and traffic movements. Moreover, it will be capable of measuring, reporting and responding to its own condition, providing instant information on weather, incidents and travel information.

Finally, the Resilient Road will be fully adaptable to extreme weather conditions and the effects of climate change. The road will be able to monitor flooding, snow, ice, wind and temperature change and will be able to adapt to their impacts through integrated storm drainage, and pavement heating and cooling. It will also be linked to an integrated information system for travellers and operators.

Already there are signs that this vision will become reality, with the Road on A Roll and the ModieSlab prefabricated road from the Netherlands; the Solar Road from Solar Roadways in the US; and, from the German organisation, BASt, floor heating that uses geothermal energy to reduce the impact on bridge decks from the effects of icing (thus reducing the need for winter maintenance) and from the effects of extreme surface temperature in the summer.

In the meantime, through the many organisations that comprise FEHRL, the Forever Open Road will cover a combination of national and multinational research activities and demonstration projects to showcase integrated technologies in real road conditions. This will facilitate knowledge transfer to ensure dissemination of new ideas and prevent unnecessary duplication.

The Forever Open Road will provide a comprehensive strategy for the development of the next generation road – a concept that can be adopted across Europe for building and maintaining our future road network. It is critical, therefore, to ensure that future research funding and support is aimed at programmes such as this, rather than continuing with the current approach to research, where incremental improvements are made in many disparate areas – which at best has little strategic oversight, and at worst, has seen improvements in one area prove detrimental to another. It will also help to develop common European standards, which will enable the Forever Open Road principles to be deployed across Europe.

¹Forum of European National Highway Research Laboratories